It could be paint only, it could be a crack. I don't like the place where it's located. It makes me think it's probably a crack. It could also be that the tire dragged mud or something and it scratched the paint.

Breaking forks are the stuff of nightmares though, so If I was unsure about it, I'd probably try to find a new fork.

Despite having a couple of carbon forks at home, I hate carbon exactly for this type of things.